1. Field of the Invention
The present invention relates generally to shovels including a motor generator that assists driving by an engine and methods of controlling the same, and more particularly to a shovel including a motor generator that assists a boom raising operation and a method of controlling the same.
2. Description of the Related Art
A conventional hybrid shovel is known that includes an engine; a hydraulic pump driven by the engine; hydraulic actuators for an excavation attachment, driven with hydraulic fluid discharged by the hydraulic pump; and a motor generator configured to perform an assist operation and a generator operation. (See, for example, International Publication No. WO 2009/157511 A1.)
This hybrid shovel determines a target engine speed different from a current engine speed in accordance with an operating load on the engine due to the hydraulic pump, and causes the motor generator to perform an assist operation or a generator operation in order to attain the target engine speed.
In this manner, the hybrid shovel described in International Publication No. WO 2009/157511 A1 improves a fuel consumption rate not only in the case of a low operating load on the engine due to the hydraulic pump but also in the case of a high operating load on the engine due to the hydraulic pump.